docs(EmbedBuilder): @readonly length (#9778)

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/discord.js/src/structures/EmbedBuilder.js

@@ -35,6 +35,7 @@ class EmbedBuilder extends BuildersEmbed {
   /**
    * The accumulated length for the embed title, description, fields, footer text, and author name.
    * @type {number}
+   * @readonly
    */
   get length() {
     return embedLength(this.data);